starting out with c++, 3 rd edition 1 chapter 7 – arrays

Starting Out with C++, 3rd Edition

1

Chapter 7 – Arrays


2

7.1 Arrays Hold Multiple values

• Unlike regular variables, arrays can hold multiple values.


3

Figure 7-1

int count Enough memory for 1 int

12345

float price Enough memory for 1 float

56.981

char letter Enough memory for 1 char

A


4

Figure 7-2


5

Table 7-1

Array Declaration Number of Elements

Size of Each Element

Size of the Array

char letters[25]; 25 1 byte 25 bytes short rings[100]; 100 2 bytes 200 bytes int miles[84]; 84 4 bytes 336 bytes float temp[12]; 12 4 bytes 48 bytes doubledDistance[1000]; 1000 8 bytes 8000 bytes


6

7.2 Accessing Array elements

• The individual elements of an array are assigned unique subscripts. These subscripts are used to access the elements.


7

Program 7-1// This program asks the user for the number of hours worked// by 6 employees. It uses a 6-element int array to store the// values.

#include <iostream.h>

void main(void){

short hours[6];

cout << "Enter the hours worked by six employees: ";cin >> hours[0];cin >> hours[1];cin >> hours[2];cin >> hours[3];


8

Program continuescin >> hours[4];cin >> hours[5];cout << "The hours you entered are:";cout << " " << hours[0];cout << " " << hours[1];cout << " " << hours[2];cout << " " << hours[3];cout << " " << hours[4];cout << " " << hours[5] << endl;

}


9

Program Output with Example Input

Enter the hours worked by six employees: 20 12 40 30 30 15 [Enter]

The hours you entered are: 20 12 40 30 30 15


10

Figure 7-7


11

Program 7-2// This program asks the user for the number of hours worked// by 6 employees. It uses a 6-element short array to store the// values. #include <iostream.h>

void main(void){

short hours[6];

cout << "Enter the hours worked by six employees: ";for (int count = 0; count < 6; count++)

cin >> hours[count];cout << "The hours you entered are:";for (count = 0; count < 6; count++)

cout << " " << hours[count];cout << endl;

}


12

Program Output with Example Input

Enter the hours worked by six employees: 20 12 40 30 30 15 [Enter]

The hours you entered are: 20 12 40 30 30 15


13

Program 7-3// This program asks the user for the number of hours worked// by 6 employees. It uses a 6-element short array to store the// values.#include<iostream.h>

void main(void){

short hours[6];

cout << "Enter the hours worked by six employees.\n";for (int count = 1; count <= 6; count++){

cout << "Employee " << count << ": ";cin >> hours[count - 1];

}cout << "The hours you entered are\n";


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Program continues

for (count = 1; count <= 6; count++){

cout << "Employee " << count << ": ";cout << hours[count - 1] << endl;

}

}


15

Program Output with Example InputEnter the hours worked by six employees.Employee 1: 20 [Enter]Employee 2: 12 [Enter]Employee 3: 40 [Enter]Employee 4: 30 [Enter]Employee 5: 30 [Enter]Employee 6: 15 [Enter]The hours you entered areEmployee 1: 20Employee 2: 12Employee 3: 40Employee 4: 30Employee 5: 30Employee 6: 15


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7.3 No Bounds Checking in C++

• C++ gives you the freedom to store data past an array’s boundaries.


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Program 7-4// This program unsafely accesses an area of memory by writing// values beyond an array's boundary.// WARNING: If you compile and run this program, it could cause// the computer to crash.#include <iostream.h>

void main(void){

short values[3]; // An array of 3 short integers.

cout << "I will store 5 numbers in a 3 element array!\n";for (int count = 0; count < 5; count++)

values[count] = 100;cout << "If you see this message, it means the computer\n";cout << "has not crashed! Here are the numbers:\n";for (int count = 0; count < 5; count++)

cout << values[count] << endl;

}


18

Figure 7-8


19

7.4 Array Initialization

• Arrays may be initialized when they are declared.


20

Program 7-5

// This program displays the number of days in each month.// It uses a 12-element int array.


void main(void){

int days[12];days[0] = 31; // Januarydays[1] = 28; // Februarydays[2] = 31; // Marchdays[3] = 30; // Aprildays[4] = 31; // Maydays[5] = 30; // Junedays[6] = 31; // July


21

Program continues

days[7] = 31; // Augustdays[8] = 30; // Septemberdays[9] = 31; // Octoberdays[10] = 30; // Novemberdays[11] = 31; // Decemberfor (int count = 0; count < 12; count++){

cout << "Month " << (count + 1) << " has ";

cout << days[count] << " days.\n";}

}


22

Program Output

Month 1 has 31 days.Month 2 has 28 days.Month 3 has 31 days.Month 4 has 30 days.Month 5 has 31 days.Month 6 has 30 days.Month 7 has 31 days.Month 8 has 31 days.Month 9 has 30 days.Month 10 has 31 days.Month 11 has 30 days.Month 12 has 31 days.


23

Program 7-6// This program displays the number of days in each month.// It uses a 12-element int array.#include <iostream.h>

void main(void){

int days[12] = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};for (int count = 0; count < 12; count++){

cout << "Month " << (count + 1) << " has ";cout << days[count] << " days.\n";

}}


24

Program Output

Month 1 has 31 days.Month 2 has 28 days.Month 3 has 31 days.Month 4 has 30 days.Month 5 has 31 days.Month 6 has 30 days.Month 7 has 31 days.Month 8 has 31 days.Month 9 has 30 days.Month 10 has 31 days.Month 11 has 30 days.Month 12 has 31 days.


25

Program 7-7// This program uses an array of ten characters to store the// first ten letters of the alphabet. The ASCII codes of the// characters are displayed.#include <iostream.h>

void main(void){

char letters[10] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J'};

cout << "Character" << "\t" << "ASCII Code\n";cout << "--------" << "\t" << "----------\n";for (int count = 0; count < 10; count++){

cout << letters[count] << "\t\t";cout << int(letters[count]) << endl;

}}


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Program Output

Character ASCII Code--------- ----------

A 65B 66C 67D 68E 69F 70G 71H 72I 73

J 74


27

Partial Array Initialization

• When an array is being initialized, C++ does not require a value for every element.

int numbers[7] = {1, 2, 4, 8};


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Program 7-8// This program has a partially initialized array.


void main(void){

int numbers[7] = {1, 2, 4, 8}; // Initialize the // first 4 elements.

cout << "Here are the contents of the array:\n";for (int index = 0; index < 7; index++)

cout << numbers[index] << endl;}


29

Program Output

Here are the contents of the array:1248000


30

Implicit Array Sizing

• It is possible to declare an array without specifying its size, as long as you provide an initialization list.

float ratings[] = {1.0, 1.5, 2.0, 2.5, 3.0};


31

Initializing With Strings

• When initializing a character array with a string, simply enclose the string in quotation marks:

char name[] = “Warren”;


32

Figure 7-11


33

Program 7-9// This program displays the contents of two char arrays.#include <iostream.h>

void main(void){

char name1[] = "Holly";char name2[] = {'W', 'a', 'r', 'r', 'e', 'n', '\0'};

cout << name1 << endl;cout << name2 << endl;

}


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Program Output

HollyWarren


35

7.5 Processing Array Contents

• Individual array elements are processed like any other type of variable.


36

Program 7-10// This program stores, in an array, the hours worked by 5// employees who all make the same hourly wage.


void main(void){

int hours[5];float payRate;

cout << "Enter the hours worked by 5 employees who all\n";cout << "earn the same hourly rate.\n";for (int index = 0; index < 5; index++){

cout << "Employee #" << (index + 1) << ": ";cin >> hours[index];

}


37

Program continues

cout << "Enter the hourly pay rate for all the employees: ";cin >> payRate;cout << "Here is the gross pay for each employee:\n";cout.precision(2);cout.setf(ios::fixed | ios::showpoint);for (index = 0; index < 5; index++){

float grossPay = hours[index] * payRate;cout << "Employee #" << (index + 1);cout << ": $" << grossPay << endl;

}}


38

Program Output with Example InputEnter the hours worked by 5 employees who allearn the same hourly rate.Employee #1: 5 [Enter]Employee #2: 10 [Enter]Employee #3: 15 [Enter]Employee #4: 20 [Enter]Employee #5: 40 [Enter]Enter the hourly pay rate for all the employees: 12.75

[Enter]Here is the gross pay for each employee:Employee #1: $63.75Employee #2: $127.50Employee #3: $191.25Employee #4: $255.00Employee #5: $510.00


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Program 7-11// This program stores, in an array, the hours worked by 5// employees who all make the same hourly wage. It then// displays the gross pay, including any overtime.


// Constant for defining the array size

void main(void){

int hours[5];float payRate;

cout << "Enter the hours worked by 5 employees who all\n";cout << "earn the same hourly rate.\n";for (int index = 0; index < 5; index++){

cout << "Employee #" << (index + 1) << ": ";cin >> hours[index];

}


40

Program continuescout << "Enter the hourly pay rate for all the employees: ";cin >> payRate;cout << "Here is the gross pay for each employee:\n";cout.precision(2);cout.setf(ios::fixed | ios::showpoint);for (index = 0; index < 5; index++){

float grossPay, overTime;if (hours[index] > 40){

// Calculate pay for 40 hours.grossPay = 40 * payRate; // Calculate overtime pay.overTime = (hours[index] - 40) * 1.5 *

payRate;// Add regular pay and overtime pay.grossPay += overTime;

}


41

Program continues

elsegrossPay = hours[index] * payRate;

cout << "Employee #" << (index + 1);cout << ": $" << grossPay << endl;

}}


42

Program Output with Example InputEnter the hours worked by 5 employees who allearn the same hourly rate.Employee #1: 10 [Enter]Employee #2: 20 [Enter]Employee #3: 50 [Enter]Employee #4: 40 [Enter]Employee #5: 60 [Enter]

Enter the hourly pay rate for all the employees: 12.75 [Enter]

Here is the gross pay for each employee:Employee #1: $127.50Employee #2: $255.00Employee #3: $701.25Employee #4: $510.00Employee #5: $892.50


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7.6 Focus on Software Engineering: Parallel Arrays

• By using he same subscript, you can build relationships between data stored in two or more arrays.


44

Program 7-12// This program stores, in two arrays, the hours worked by 5// employees, and their hourly pay rates.#include <iostream.h>

// Constant for defining the array sizeconst int numEmps = 5;

void main(void){

int hours[numEmps];float payRate[numEmps];

cout << "Enter the hours worked by “ << numEmps << “ employees and their\n";

cout << "hourly rates.\n"; for (int index = 0; index < numEmps; index++){

cout << "hours worked by employee #" << (index + 1);cout << ": ";


45

Program continues

cin >> hours[index];cout << "Hourly pay rate for employee #";cout << (index + 1) << ": ";cin >> payRate[index];

}cout << "Here is the gross pay for each employee:\n";cout.precision(2);cout.setf(ios::fixed | ios::showpoint);for (index = 0; index < numEmps; index++){

float grossPay = hours[index] * payRate[index];cout << "Employee #" << (index + 1);cout << ": $" << grossPay << endl;

}}


46

Program Output with Example InputEnter the hours worked by 5 employees and their hourly

rates.hours worked by employee #1: 10 [Enter]Hourly pay rate for employee #1: 9.75 [Enter]hours worked by employee #2: 15 [Enter]Hourly pay rate for employee #2: 8.62 [Enter]hours worked by employee #3: 20 [Enter]Hourly pay rate for employee #3: 10.50 [Enter]hours worked by employee #4: 40 [Enter]Hourly pay rate for employee #4: 18.75 [Enter]hours worked by employee #5: 40 [Enter]Hourly pay rate for employee #5: 15.65 [Enter]

Here is the gross pay for each employee:Employee #1: $97.50Employee #2: $129.30Employee #3: $210.00


47

7.7 Thou Shalt Not Assign

• You cannot use the assignment operator to copy one array’s contents to another.

for (int count=0; count < 4; count++)

newVal[count] = oldVal[count];


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Table 7-2

Expression Value

O ld V alues[0 ] 10 (Contents of Element 0 of O ld V alues)




N ew V alues 8012 (Memory Address of N ew V alues)

O ld V alues 8024 (Memory Address of O ld V alues)


49

7.8 Printing the Contents of an Array

• To display the contents of an array, you must use a loop to display the contents of each element.

int array[5] = { 10, 20, 30, 40, 50 };for (int count = 0; count < 5; count++)

cout << array[count] << endl;


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7.9 Arrays As Function Arguments

• To pass an array as an argument to a function, pass the name of the array.


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Program 7-13// This program demonstrates that an array element is passed// to a function like any other variable.#include <iostream.h>

void ShowValue(int); // Function prototype

void main(void){

int collection[8] = {5, 10, 15, 20, 25, 30, 35, 40};

for (int Cycle = 0; Cycle < 8; Cycle++)ShowValue(collection[Cycle]);

}


52

Program continues

//************************************// Definition of function showValue. *// This function accepts an integer argument. *// The value of the argument is displayed. *//************************************void ShowValue(int Num){

cout << Num << " ";}


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Program Output

5 10 15 20 25 30 35 40


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Program 7-14// This program demonstrates an array being passed to a function.#include <iostream.h>

void showValues(int []); // Function prototype

void main(void){

int collection[8] = {5, 10, 15, 20, 25, 30, 35, 40};

showValues(collection); // Passing address of array collection}

//***********************************************// Definition of function showValues. *// This function accepts an array of 8 integers *// as its argument. The contents of the array *// is displayed. *//***********************************************void showValues(int nums[]){

for (int index = 0; index < 8; index++)cout << nums[index] << " ";

}


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Program Output

5 10 15 20 25 30 35 40


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Program 7-15// This program demonstrates an array being passed to a function.#include <iostream.h>

void showValues(int []); // Function prototype

void main(void){

int set1[8] = {5, 10, 15, 20, 25, 30, 35, 40};int set2[8] = {2, 4, 6, 8, 10, 12, 14, 16};showValues(set1);cout << endl;showValues(set2);

}

//***********************************************// Definition of function showValues. *// This function accepts an array of 8 integers *// as its argument. The contents of the array *// is displayed. *//***********************************************void showValues(int nums[]){

for (int index = 0; index < 8; index++)cout << nums[index] << " ";

}


57

Program Output

5 10 15 20 25 30 35 402 4 6 8 10 12 14 16


58

Program 7-16// This program uses a function that can display the contents// of an integer array of any size.#include <iostream.h>

void showValues(int [], int); // Function prototype

void main(void){

int set1[8] = {5, 10, 15, 20, 25, 30, 35, 40};int set2[4] = {2, 4, 6, 8};int set3[12] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};

showValues(set1, 8);cout << endl;showValues(set2, 4);cout << endl;showValues(set3, 12);

}


59

Program continues

//***********************************************// Definition of function showValues. *// This function displays the contents of the *// array passed into nums. The value passed *// into elements is the number of elements in *// the nums array. *//***********************************************

void showValues(int nums[], int elements){

for (int index = 0; index < elements; index++)cout << nums[index] << " ";

}


60

Program Output

5 10 15 20 25 30 35 402 4 6 81 2 3 4 5 6 7 8 9 10 11 12


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Program 7-17// This program uses a function that doubles the contents of// the elements within an array.#include <iostream.h>

void doubleArray(int [], int); // Function prototypeconst int arraySize = 12;

void main(void){

int set[arraySize] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};cout << "The arrays values are:\n";for (int index = 0; index < arraySize; index++)

cout << set[index] << " ";cout << endl;doubleArray(set, arraySize);cout << "After calling doubleArray, the values are:\n";


62

Program continuesfor (int index = 0; index < arraySize; index++)

cout << set[index] << " ";cout << endl;

}

//**************************************************// Definition of function doubleArray. *// This function doubles the value of each element *// in the array passed into nums. *// The value passed into size is the number of *// elements in the nums array. *//**************************************************void doubleArray(int nums[], int size){

for (int index = 0; index < size; index++)nums[index] *= 2;

}


63

Program Output

The array values are:1 2 3 4 5 6 7 8 9 10 11 12After calling doubleArray, the values are:2 4 6 8 10 12 14 16 18 20 22 24


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7.10 Two-dimensional Arrays

• A two-dimensional array is like several identical arrays put together. It is useful for storing multiple sets of data.


65

Program 7-18// This program demonstrates a two-dimensional array.


void main(void){

float sales[3][4]; // 2D array, 3 rows and 4 columns.float totalSales = 0; // To hold the total sales.int dir, qtr; // Loop counters.


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Program continuescout << "This program will calculate the total sales of\n";cout << "all the company's divisions.\n";cout << "Enter the following sales information:\n\n";

// Nested loops to fill the array with quarterly// sales figures for each division.for (div = 0; div < 3; div++){

for (qtr = 0; qtr < 4; qtr++){

cout << "Division " << (div + 1);cout << ", Quarter " << (qtr + 1) << ": $";cin >> sales[div][qtr];

}cout << endl; // Print blank line.

}


67

Program continues

// Nested loops to add all the elements.for (div = 0; div < 3; div++)

for (qtr = 0; qtr < 4; qtr++)totalSales += sales[div][qtr];

cout.precision(2);cout.setf(ios::fixed | ios::showpoint);cout << "The total sales for the company are: $";cout << totalSales << endl;

}


68

Program Output with Example InputThis program will calculate the total sales ofall the company's divisions.Enter the following sales information:

Division 1, Quarter 1: $31569.45 [Enter]Division 1, Quarter 2: $29654.23 [Enter]Division 1, Quarter 3: $32982.54 [Enter]Division 1, Quarter 4: $39651.21 [Enter]



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Output continues


The total sales for the company are: $456782.34


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Passing Two-dimensional Arrays to Functions

• When a two-dimensional array is passed to a function, the parameter type must contain a size declarator for the number of columns.


71

7.11 Arrays of Strings

• A two-dimensional array of characters can be used as an array of C-strings.


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Program 7-20// This program displays the number of days in each month.// It uses a two-dimensional character array to hold the // names of the months and an int array to hold the number// of days.#include <iostream.h>

void main(void){

char months[12][10] = {"January", "February", "March", "April", "May", "June",

"July", "August", "September”, "October", "November","December"};int days[12] = { 31, 28, 31, 30,

31, 30, 31, 31, 30, 31, 30, 31};

for (int count = 0; count < 12; count++){

cout << months[count] << " has ";cout << days[count] << " days.\n";

}}


73

Program 7-20 (continued)

Program OutputJanuary has 31 days.February has 28 days.March has 31 days.April has 30 days. May has 31 days. June has 30 days. July has 31 days.August has 31 days. September has 30 days. October has 31 days. November has 30 days.December has 31 days.


74

Three Dimensional Arrays and Beyond

• C++ allows you to create arrays with virtually any number of dimensions.

• Here is an example of a three-dimensional array declaration:

float seat[3][5][8];


75

7.14 Introduction to the STL vector

• The Standard Template Library (or STL) is a collection of data types and algorithms that you may use in your programs. These data types and algorithms are programmer-defined. They are not part of the C++ language, but were created in addition to the built-in data types.


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• The data types that are defined in the STL are commonly called containers, because they store and organize data.

• There are two types of containers in the STL: sequence containers and associative containers.

• The vector data type is a sequence container.


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• A vector is like an array in the following ways:– A vector holds a sequence of values, or

elements.– A vector stores its elements in contiguous

memory locations.– You can use the array subscript operator [] to

read the individual elements in the vector


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• However, a vector offers several advantages over arrays. Here are just a few:– You do not have to declare the number of

elements that the vector will have. – If you add a value to a vector that is already

full, the vector will automatically increase its size to accommodate the new value.

– vectors can report the number of elements they contain.


79

Declaring a vector

• To use vectors in your program, you must first #include the vector header file with the following statement:

#include <vector>

Note: There is no .h at the end of the file name.


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Declaring a vector

• The next step is to include the following statement after your #include statements:

using namespace std;

The STL uses namespaces to organize the names of its data types and algorithms.


81

Declaring a vector

• Now you are ready to declare an actual vector object. Here is an example:

vector<int> numbers;

The statement above declares numbers as a vector of ints.


82

Declaring a vector

• You can declare a starting size, if you prefer. Here is an example:

vector<int> numbers(10);

The statement above declares numbers as a vector of 10 ints.


83

Other examples of vector Declarations

Declaration Format Description

vector<float> amounts; Declares amounts as an empty vector of floats.

vector<int> scores(15); Declares scores as a vector of 15 ints.

vector<char> letters(25, 'A'); Declares letters as a vector of 25 characters. Each element is initialized with 'A'.

vector<double> values2(values1); Declares values2 as a vector of doubles. All the elements of values1, which also a vector of doubles, are copied to value2.


84

Storing and Retrieving Values in a vector

• To store a value in an element that already exists in a vector, you may use the array subscript operator [].


85

Program 7-23// This program stores, in two vectors, the hours worked by 5// employees, and their hourly pay rates.#include <iostream.h>#include <vector> // Needed to declare vectorsusing namespace std;

void main(void){

vector<int> hours(5); // Declare a vector of 5 integersvector<float> payRate(5); // Declare a vector of 5 floats

cout << "Enter the hours worked by 5 employees and their\n";cout << "hourly rates.\n";for (int index = 0; index < 5; index++){

cout << "Hours worked by employee #" << (index + 1);cout << ": ";cin >> hours[index];cout << "Hourly pay rate for employee #";cout << (index + 1) << ": ";cin >> payRate[index];

}


86

Program 7-23 (continued)cout << "Here is the gross pay for each employee:\n";cout.precision(2);cout.setf(ios::fixed | ios::showpoint);for (index = 0; index < 5; index++){ float grossPay = hours[index] * payRate[index];

cout << "Employee #" << (index + 1);cout << ": $" << grossPay << endl;

}}


87

Program 7-23 (continued)Program Output with Example Input Shown in Bold

Enter the hours worked by 5 employees and theirhourly rates.Hours worked by employee #1: 10 [Enter]Hourly pay rate for employee #1: 9.75 [Enter]Hours worked by employee #2: 15 [Enter]Hourly pay rate for employee #2: 8.62 [Enter]Hours worked by employee #3: 20 [Enter]Hourly pay rate for employee #3: 10.50 [Enter]Hours worked by employee #4: 40 [Enter]Hourly pay rate for employee #4: 18.75 [Enter]Hours worked by employee #5: 40 [Enter]Hourly pay rate for employee #5: 15.65 [Enter]Here is the gross pay for each employee:Employee #1: $97.50Employee #2: $129.30Employee #3: $210.00Employee #4: $750.00Employee #5: $626.00


88

Using the push_back Member Function

• You cannot use the [] operator to access a vector element that does not exist.

• To store a value in a vector that does not have a starting size, or is already full, use the push_back member function. Here is an example:

numbers.push_back(25);


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Program 7-24// This program stores, in two vectors, the hours worked by a specified// number of employees, and their hourly pay rates.

#include <iostream.h>#include <vector> // Needed to declare vectorsusing namespace std;

void main(void){

vector<int> hours; // hours is an empty vectorvector<float> payRate; // payRate is an empty vectorint numEmployees; // The number of employees

cout << "How many employees do you have? ";cin >> numEmployees;cout << "Enter the hours worked by " << numEmployees;cout << " employees and their hourly rates.\n";


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Program 7-24 (continued)for (int index = 0; index < numEmployees; index++){

int tempHours; // To hold the number of hours enteredfloat tempRate; // To hold the payrate entered

cout << "Hours worked by employee #" << (index + 1);cout << ": ";cin >> tempHours;hours.push_back(tempHours); // Add an element to hourscout << "Hourly pay rate for employee #";cout << (index + 1) << ": ";cin >> tempRate;payRate.push_back(tempRate); // Add an element to payRate

}cout << "Here is the gross pay for each employee:\n";cout.precision(2);cout.setf(ios::fixed | ios::showpoint);for (index = 0; index < numEmployees; index++){

float grossPay = hours[index] * payRate[index];cout << "Employee #" << (index + 1);cout << ": $" << grossPay << endl;

}}


91


How many employees do you have? 3 [Enter] Enter the hours worked by 3 employees and their hourly rates.Hours worked by employee #1: 40 [Enter]Hourly pay rate for employee #1: 12.63 [Enter]Hours worked by employee #2: 25 [Enter]Hourly pay rate for employee #2: 10.35 [Enter]Hours worked by employee #3: 45 [Enter]Hourly pay rate for employee #3: 22.65 [Enter]Here is the gross pay for each employee:Employee #1: $505.20Employee #2: $258.75Employee #3: $1019.25


92

Determining the Size of a vector

• Unlike arrays, vectors can report the number of elements they contain. This is accomplished with the size member function. Here is an example of a statement that uses the size member function:

numValues = set.size();

• In the statement above, assume that numValues is an int, and set is a vector. After the statement executes, numValues will contain the number of elements in the vector set.


93

Determining the Size of a vector

• Example:

void showValues(vector<int> vect){

for (int count = 0; count < vect.size(); count++)cout << vect[count] << endl;

}


94

Program 7-25// This program demonstrates the vector size // member function.#include <iostream.h>

#include <vector>using namespace std; // Function prototypevoid showValues(vector<int>); void main(void){

vector<int> values;

for (int count = 0; count < 7; count++)values.push_back(count * 2);

showValues(values);}


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Program 7-25 (continued)//**************************************************// Definition of function showValues. *// This function accepts an int vector as its *// argument. The value of each of the vector's *// elements is displayed. *//************************************************** void showValues(vector<int> vect){

for (int count = 0; count < vect.size(); count++)cout << vect[count] << endl;

}


96


Program Output 024681012


97

Removing Elements from a vector

• Use the pop_back member function to remove the last element from a vector.

collection.pop_back(); The statement above removes the last element from the collection vector.


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Program 7-26// This program demosntrates the vector size member function. #include <iostream.h>#include <vector>using namespace std; void main(void){

vector<int> values;

// Store values in the vectorvalues.push_back(1);values.push_back(2);values.push_back(3);cout << "The size of values is " << values.size() << endl;

// Remove a value from the vectorcout << "Popping a value from the vector...\n";values.pop_back();cout << "The size of values is now " << values.size() << endl;


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Program 7-26 (continued)// Now remove another value from the vectorcout << "Popping a value from the vector...\n";values.pop_back();cout << "The size of values is now " << values.size() << endl;

// Remove the last value from the vectorcout << "Popping a value from the vector...\n";values.pop_back();cout << "The size of values is now " << values.size() << endl;

}

Program Output

The size of values is 3Popping a value from the vector...The size of values is now 2Popping a value from the vector...The size of values is now 1Popping a value from the vector...The size of values is now 0


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Clearing a vector

• To completely clear the contents of a vector, use the clear member function. Here is an example:

numbers.clear(); After the statement above executes, the numbers vector will be cleared of all its elements.


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Program 7-27// This program demosntrates the vector size member function.#include <iostream.h>#include <vector>using namespace std; void main(void){

vector<int> values(100);

cout << "The values vector has “<< values.size() << " elements.\n";

cout << "I will call the clear member function...\n";values.clear();cout << "Now, the values vector has “

<< values.size() << " elements.\n";}


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Program Output The values vector has 100 elements.I will call the clear member function...Now, the values vector has 0 elements.


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Detecting an Empty vector

• To determine if a vector is empty, use the empty member function. The function returns true if the vector is empty, and false if the vector has elements stored in it. Here is an example of its use:

if (set.empty())cout << "No values in set.\

n";


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Program 7-28// This program demosntrates the vector's empty member function. #include <iostream.h>#include <vector>using namespace std; // Function prototypefloat avgVector(vector<int>); void main(void){

vector<int> values;int numValues;float average;

cout << "How many values do you wish to average? ";cin >> numValues;


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Program 7-28 (continued)for (int count = 0; count < numValues; count++){

int tempValue;

cout << "Enter a value: ";cin >> tempValue;values.push_back(tempValue);

}average = avgVector(values);cout << "Average: " << average << endl;

} //*************************************************************// Definition of function avgVector. *// This function accepts an int vector as its argument. If *// the vector contains values, the function returns the *// average of those values. Otherwise, an error message is *// displayed and the function returns 0.0. *//*************************************************************


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Program 7-28 (continued)float avgVector(vector<int> vect){

int total = 0; // accumulatorfloat avg; // average

if (vect.empty()) // Determine if the vector is empty{

cout << "No values to average.\n";avg = 0.0;

}else{

for (int count = 0; count < vect.size(); count++)total += vect[count];

avg = total / vect.size();}return avg;

}


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How many values do you wish to average?Enter a value: 12Enter a value: 18Enter a value: 3Enter a value: 7Enter a value: 9Average: 9

Program Output with Example Input Shown in Bold

How many values do you wish to average? 0No values to average.Average: 0


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Summary of vector Member Functions

Member Function Description

at(element) Returns the value of the element located at element in the vector. Example:x = vect.at(5);The statement above assigns the value of the 5th element of vect to x.

capacity() Returns the maximum number of elements that may be stored in the vector without additional memory being allocated. (This is not the same value as returned by the size member function).Example:x = vect.capacity();The statement above assigns the capacity of vect to x.


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clear() Clears a vector of all its elements.Example:vect.clear();The statement above removes all the elements from vect.

empty() Returns true if the vector is empty. Otherwise, it returns false.Example:if (vect.empty()) cout << "The vector is empty.";The statement above displays the message if vect is empty.

pop_back() Removes the last element from the vector.Example:vect.pop_back();The statement above removes the last element of vect, thus reducing its size by 1.


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push_back(value) Stores a value in the last element of the vector. If the vector is full or empty, a new element is created.Example:vect.push_back(7);The statement above stores 7 in the last element of vect.

reverse() Reverses the order of the elements in the vector (the last element becomes the first element, and the first element becomes the last element.)Example:vect.reverse();The statement above reverses the order of the element in vect.

resize(elements, value)

Resizes a vector by elements elements. Each of the new elements is initialized with the value in value.Example:vect.resize(5, 1);The statement above increases the size of vect by 5 elements. The 5 new elements are initialized to the value 1.


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swap(vector2) Swaps the contents of the vector with the contents of vector2.Example:vect1.swap(vect2);The statement above swaps the contents of vect1 and vect2.

starting out with c++, 3 rd edition 1 chapter 7 – arrays

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